1. Field of the Invention
This invention relates to a process and apparatus for achieving chaotic mixing of fluid flow through a coiled section of a tubular member for enhancing in-tube heat transfer, wherein the fluid flow is directed through a helical arrangement including coils having their corresponding coil axes positioned at some angle with respect to each other.
2. Description of Prior Art
Hydrodynamics of chaotic particle paths have been discussed within various publications, such as: Jones, Scott W., et al., Chaotic Advection by Laminar Flow in a Twisted Pipe, Journal of Fluid Mechanics, Vol. 209, p. 335 (1989), which states that chaotic advection of a passive scalar in steady laminar flow through a sequence of pipe bends leads to enhanced transverse and longitudinal stirrings, which is important to applications such as heat and mass transfer in piping systems; and Peerhossaini, H., et al., Chaotic Motion in the Dean Instability Flow--A Heat Exchanger Design, Bulletin of the American Physical Society, Program of the 43rd Annual Meeting of the Division of Fluid Dynamics, Vol. 35, No. 10, p. 2229 (1990). In Order Breaking in Dean Flow, Phys. Fluids A, Vol. 3, No. 5, p. 1029 (May 1991), Le Guer, Yves, et al. discuss combining large vortical structures in the flow with the dynamical behavior of open systems to enhance heat transfer and mixing, particularly in an apparatus having a succession of curved channels in which the curvature plane rotates 90.degree. between each of two adjacent curved elements. Although such reference suggests that chaotic mixing is expected to enhance the advection of passive scalars and therefore improve the efficiency of heat transfer from the walls, such reference only discusses heat transfer with respect to laminar flow and does not even suggest the impact of chaotic mixing in a turbulent flow regime.
Other references have discussed increasing in-tube heat transfer by various mechanical methods. For example, U.S. Pat. No. 2,115,769 teaches a radiant heating tube which has spiral grooves or corrugations along which burning gases are whirled and eddied. The centrifugal forces cause the burning gases to swirl as they pass through the conduit.
U.S. Pat. No. 4,444,357 teaches a method and apparatus for mixing two input streams at different temperatures to form an intermediate combined stream at a regulated temperature. A heat exchange coil acts as a quick-response, continuous-flow heat exchanger, which alternately extracts and returns heat from differing-temperature pulses as the same merge and blend through their travel within the coil.
U.S. Pat. No. 4,469,446 discloses a fluid handling apparatus which has a plurality of hollow airfoil shaped vanes which are positioned within a first gaseous stream, and a second gaseous stream is conveyed through the hollow vane and is discharged into the first stream through a slot at the trailing edge of the vane.
Conventional passive techniques for enhancement of in-tube conventional heat transfer can be roughly classified into two categories: (1) increased effective heat transfer area; and (2) increased mixing methods. External and internal fins fall into the former category of conventional art, while the latter category of conventional art includes increased turbulence intensity and increased unsteady flow through inserts of various kinds, regular mixing in recirculation zones and resonant enhancement of flow instabilities. Some devices, of course, do both.
It is apparent that conventional technology and prior art references consider only chaotic fluid flow as it relates to flow within the laminar regime. It is very likely that persons skilled in the art of fluid mechanics and heat and mass transfer have not considered the effects of chaotic mixing of flow within a turbulent regime, since it would be expected that the increased energy requirements for pressure drops associated with turbulent flow would far outweigh any energy benefits realized through increased heat exchange efficiency.